Accident Prevention The Use of Hoses & Hard-Arms at Marine Terminals Handling Liquefied Gas

Dive into our in-depth article on the hazards and accidents at marine terminals handling LNG and LPG. We cover essential topics including accident summaries, key hazards, and the importance of safe berthing and mooring practices.

Discover best operational procedures and ship maneuvering techniques in harbor areas to mitigate risks. This resource is designed for industry stakeholders aiming to improve safety standards and operational protocols in the handling of liquefied gases at marine terminals.

Introduction

Members attending a SIGTTO Panel meeting in 1995 requested an update of Information Paper No.4 (first published in 1987) and entitled Incidents Involving the Use of Hoses and Marine Loading Arms for the Transfer of Liquefied Gases Accordingly, new research was carried out and this document was presented for approval In its new format It is for general circulation.

Preamble

The report is addressed mainly to terminal operators but some aspects could be of direct relevance to ship operators.

The report covers accidents and near-misses at the ship/shore interface involving either hoses or hard-arms. It covers the LNG, LPG and chemical gas trades but only lightly touches upon the smaller scale barge-type operations. Regarding the accident data, the period covered varies with the type of accident but in general SIGTTO’s data-base becomes more reliable after 1982 (for accident information prior to this a reference is available) Apart from issues directly related to hard-arms and hoses, the study, by its nature, also includes ship/shore mooring security and spill-limitation devices: both these subjects having direct relevance to the security of the cargo connection.

Accident data from the earlier report is incorporated into this publication. In addition SIGTTO has called on its in-house data-base for newer information and recent feedback has been obtained from the membership to cover current experience. This data is summarized in Appendix 1*** but, for reasons of confidentiality, the listing omits the source of information and manufactures names.

It is hoped that the new data coverage in this publication dovetails well with the earlier edition thus capturing most well known events into one document. However, readers are advised that this may not always be the case as reporting in the earlier years was incomplete, and even today it could be more comprehensive; particularly for the less serious events. Also there is a strong probability, particularly for the LPG and chemical gas trades, that some data is lacking:

1. Firstly, this is because spills in the manifold area only attract international attention either where there is significant damage to a ship or where grave accident has happened to personnel;
2. Secondly, it may be due to the more fragmented nature of that trade.

Therefore, as a record of all such gas spillages and near-miss incidents, the data provided in Appendix 1*** must be considered incomplete and attempts made to quantify the risk can only underestimate.

A reference (see Section 10***) includes an interesting addition to the armoury of recommendations available to terminal management. This covers marine terminal audits. As noted in one of the accident reports, the terminal concerned was unaware of appropriate auditing standards. Accordingly, terminal managers will benefit from following the guidance given. Such a programme for auditing Terminal Operations for LNG or LPG Carrier after Arriving in Portmarine terminal operations is recommended by SIGTTO.

Scope

This category of articles cover accidents relating to hoses, hard-arms and pipeline incidents close to ship or shore manifolds. The report only covers the liquefied gas industry. Where possible, and resulting from incidents, the design and operation of various equipment types is discussed. Important lessons learned are included.

As some of the data input ts limited in extent it has not always been possible to draw firm conclusions Or to positively identify the most likely causes of the accident. In some such cases assumptions have been made and the most likely solutions suggested.

This category dwells on a number of central factors. Firstly the good quality of Emergency Mooring Release of Liquefied Gas Carriersmooring systems are emphasized. Secondly, Emergency Shut-Down systems and Emergency Release Couplers are covered. An aim ts to achieve, by combination of these facilities, a ship/shore pumping system which reduces the chance of serious spillage (having probability of ignition) to the realms of a non-credible event.

Accident Summary

A review of the accidents on SIGTTO’s data-base shows that the frequency of serious events is rare incidents to gas carriers do not happen often. Nevertheless, for the gas trades, the frequency of accidents, related to the cargo manifold, represent an important area of risk which should be addressed.

For the analysis shown in the following table a serious event is one having caused death, personal injury or major equipment damage. Serious events also include cases where such a casualty was only narrowly averted.

The table also outlines the main hazards as found from actual accident data and ascribes a qualitative risk to those hazards.

Note: It should be appreciated that the Findings and Suggested Procedures, as discussed below, follow from the analysis of accidents known to SIGTTO it could be that risk analysis or common sense including a more holistic view, to include human error, might suggest more stringent precautions in some cases.

Findings:

• Compared with hard-arms, the use of flexible hose for cargo transfer has resulted in a disproportionately high number of fatalities and injuries.
• Ships breaking-out from their berths are confined mainly to carriers of over 50 000 m³ capacity. These are serious events which may be occurring as often as twice per year.
• In some ports the operation and maintenance of hard-arms and QCDCs ts shown to be below standard There are accidents on record attesting to this aspect.
• Questions related to surge pressures seem to be poorly understood at some terminals and this has caused accidents.

Suggested procedures:

• Terminals should have a proper schedule to enable the purchase and selection of the correct hose type for cargo pressure, temperature and grade.
• Cargo hoses should be specially well inspected and tested at suitable intervals and, before use, cargo hoses should be inspected visually.
• Terminals handling ships of over 30 000 m³ should use hard-arms and have an Emergency Release Coupling (ERC) fitted within the arm (see Table 9.2***). Terminals handling smaller ships may also benefit from this recommendation; however, accident reports for this class of ship are too few to satisfactorily quantify.
• Terminals using hard-arms should provide inter-linkable ESD equipment to ensure that, in an emergency, ship and shore shut-down can be accomplished safely.
• Terminals should establish ship-size limits for their berths. They should also prepare individual mooring plans for each new ship (especially those of over 50 000 m³) coming to their berths. To ensure a safe mooring can be achieved, the joint ship/shore mooring plan should be subject to computer analysis (see Section 4.3***).
• Terminals should have operational procedures and individualized Jetty Regulations that cover mooring emergencies such as strong winds.
• Terminals should ensure that operations and maintenance personnel are well trained on the hard-arms fitted.
• Terminals should check that cargo pipeline systems have undergone an hydraulic analysis, that ESD (Emergency Shut-Down) valve closure times are in accordance with the findings of the analysis and that pipeline systems are in accord with SIGTTO’s recommendations.

The Hazards

For cargo operations at marine terminals, records show that the greatest nsk of serious gas escape is concentrated at the ship and shore manifold area. This may result from a ship breaking-out from the berth, typically due to strong wind conditions, although strong currents, and even ice conditions, have caused similar problems. Accidents have also occurred because of human error, lack of training, failure of hoses and the malfunction of hard-arms. A further cause is shown to result from li-maintained transfer equipment.

The main elements of risk, as found from the accident data in Appendix 1, can be summarized as follows:

Conventional wisdom suggests that hard-arms are a safer option than flexible hoses for the transfer of liquefied gases. This is difficult to prove or disprove from the results of this inquiry because of limited data. It is however clear that incidents involving hoses have had the most serious consequences (although the equipment in use at the time may have been III-specified or III-maintained). On the other hand a few similar accidents have been attributed to hard-arm operation mainly due to maloperation or maintenance issues. Bearing these factors in mind and the general comments in Sections 5 and 6***, it’s clear that there is a trend towards greater use of hard-arms. From SIGTTO’s perspective, there is a strong case for using hard-arms for all ships.

The principal danger from a liquefied gas spill is the formation of a vapour cloud. These may be flammable and toxic in nature and can be very extensive. Spill volumes can be effectively limited to very small amounts by fitting in-line safety devices on hard-arms (see Section 7***), without such equipment, In case of accident, the cloud and its flammable envelope can extend for several hundreds of meters. Accordingly, where appropriate equipment’s not fitted, ignition and flash-back can pose real dangers over an area beyond the normal operational safety distances. Experience shows that fires of this nature have caused fatalities and can be extensive. There are just two known fires of this type (however, other serious spills involving ammonia are recorded).

Other dangers include the risk of very cold liquid landing on the human body causing serious frostbite and possibly chemical burns as well. In addition, a spillage of a cryogenic liquid can cause metal embrittlement to ship and shore structures. For some ships, this has resulted in their removal from service for steel renewal. These particular hazards are discussed in greater detail in other publications.

The primary means of risk reduction at the cargo manifold are:

• The provision of a safe berth, clear from other manoeuvring ships;
• A well designed mooring system (with appropriate operating procedures);
• Properly specified cargo handling equipment;
• Means of spill limitation built into the transfer equipment;
• The provision of a linked ship/shore emergency shut-down system;
• Methods of surge pressure alleviation;
• Restricted areas around ship and shore manifolds;
• Well organized handling, maintenance and testing procedures, and;
• Good training – particularly for operations personnel.

All these matters are discussed In the following sections.

Safe Berths, Mooring & Operating Procedures

The gas industry has been aware of the need for safe mooring systems for many years. The concern is akin to that expressed in the oil industry. Mooring systems have to be secure. For a moored gas carrier, good moorings are the first line of defence against a ship’s unexpected break-out from a berth and therefore have a direct bearing on the security of the cargo connection. A second line of defence, which can be the emergency release coupling (ERC) is discussed later in this category.

Read also: Emergency Procedures on Terminal and First Aid to Victims

Whereas a principal concern in the oil trade is oil pollution; in the gas trade the main concern is spillage. In both trades however It is obviously unsafe to allow a ship to break-away from her berth – even although instant readiness is usually required from the ship’s engines. A ship drifting helplessly in the seaway could quickly cause damage to adjacent craft or run aground with serious consequences.

Ship Manoeuvres in Harbour Areas

There are a number of casualties and near-miss accidents recorded for harbour channels and basins. As will be seen from Appendix 1***, some ships manoeuvring nearby have come into collision with moored gas carriers. Apart from the danger of collision, ships passing nearby and at speed can cause suction and ranging problems to a gas carrier alongside which could cause break-out.

At some terminals it is known that cargo operations are required to cease while other ships are manoeuvring nearby. It is recommended that terminal managers assess the navigational dangers at their berths to ensure that ships manoeuvring nearby attract the minimum of risk.

Exclusion Zones are often recommended around gas carrier berths to limit the approach of unauthorised small craft.

Moorings and Ship Size Limits

Safe moorings are the direct concern of shipowners, shipmasters and terminal managers. Ships should be designed, equipped and operated to suitable standards. Terminal mooring equipment should similarly established bearing in mind the recommendations of OCIMF. Furthermore, the Suitable matching of a particular berth to a particular ship is a matter which should always be addressed so that only appropriate ships are accepted.

In this regard, the suitability of a ship’s mooring complement should be checked by terminals before a ship new to the terminal is accepted for service. This is best done by Ship to Shore Access Guidelines for Gas Terminal and Vessel Operatorsterminal management who should check the ship’s mooring plan against the mooring plan for the berth. It is only by this means, now possible with user-friendly computer programs, that the proper geometry of the mooring lines can be ascertained.

One incident is known to have resulted from inattention to this aspect and this is described in the following paragraphs.

The diagram below (Fig. 1) depicts a well balanced mooring system where the mooring line geometry at each end of the ship is mirrored.

In studying this drawing reference should also be made to the next diagram (Fig. 2) where lesser qualities are explained.

In the diagram above (Fig. 2) the essential points for improvement include:

• The lack of good mooring line geometry;
• The lack of mooring lines to hold the ship from moving ahead;
• The short length of spring lines.

The essential points of a good mooring plan are:

1. That itis well-balanced having mooring lines of similar materials similarly directed from each end of the ship, and;
2. That mooring line strength and direction is suitable to hold the ship securely alongside under the forces imposed by the strongest design conditions. In weather conditions stronger than the established design criteria, it will be necessary for the ship to leave the berth.

Apart from the need for individual mooring plans, terminal management should have clear restrictions on the size of ship they can accept on their berths. One such control can be the maximum allowable ship’s windage area; another may be sea-state related For large LNG ships the sea-state is normally limited to a maximum wave height of 1,5 m and a wave period (time of peak to peak passage) of 9 seconds.x. Furthermore, berths should be designed to a sufficient strength having regard to specific maximum design criteria. One such is the displacement tonnage of the largest ship. The berth should be designed bearing in mind the speed of approach during berthing and the angle of approach set against the ship’s displacement.

While restrictions usually concern a maximum size, in some cases, there may also be a minimum ship-size stipulation. A lower restriction can come about, for example, where breasting dolphins are set far apart as tnis may provide insufficient support for small ships – where the distance along the flat of the ship’s side (parallel body) is insufficient. Equally, a small ship can be unsuited to a large ship jetty when mooring lines have to be led-up to the jetty deck at sharp angles or, in other cases, where the peculiarities of a small ship’s equipment do not lend themselves to a larger berth.

It is important for terminals to appreciate the strength of the elements acting on moored ships anc to provide mooring hooks of sufficient strength to cater for the worst conditions. Terminals should also appreciate the limitation of ship’s mooring equipment and, if extraordinary circumstances can occur at the berth, then an option may be to provide supplemental shore-based mooring lines.

Operations and Operational Procedures

Once mooring plans have been prepared it is often important that they be agreed with harbour pilots who will be the people directing ship and mooring gang during berthing operations. This is not always the case in the LNG trade where it can sometimes be found that mooring patterns are agreed between the ship operator and the terminal. In these cases, it may be the shipmaster who is advising on mooring line deployment. However, it can be found that, without support from pilots, agreed mooring plans are seldom achieved in practice.

The use of well maintained mooring equipment, both on board ship and at terminals, is vital for minimising risk. This should be a matter carefully addressed, not only on a programmed basis within the terminal but also after each ship berthing, when Parts “A” and “C” of the Ship/Shore Safety Check List are completed.

The quality and longevity of some mooring lines is also a point of concern. In particular, in some trades the use of nylon tails is encouraged as an extension to wire moorings. According to many operational procedures (as adopted by ship operators), these tails are often subject to a maximum number of hours usage before being replaced. It has been shown that such materials can be weakened by continuous high-level cyclic loading or by excessive rotation from steel wire rope. To avoid this problem time constraints should be set for the number of hours tn service so that the tails can be replaced in good time. Furthermore, some ship operators routinely “end-for-end” mooring wires to avoid premature failure at the spliced eyes and, in some cases, routinely replace mooring wires to avoid service failure. A number of minor accidents attributed to this effect have been reported, however, they are not included in Appendix 1***.

The preparation of terminal operating procedures for the berth is also important. Here it is vital to have wind limits established. This is a terminal responsibility. Limits should be set for:

• Berthing (by experience);
• The stopping of cargo pumping;
• Hard-arm removal (according to manufacturers recommendations), and;
• Berth tenability (by calculation).

These limits can be related to wind direction. For example, on the question of berth tenability, if the wind is in an off-shore direction the maximum wind speed allowable will probably be more strict than if the wind is in an on-shore direction.

In this respect it is always important for terminals to have access to local weather forecasts. Winds can be influenced by local topography and these matters may be unfamiliar to shipmasters.

To assist in operational control it is commonly found (especially at LNG terminals) that jetties are provided with load monitoring devices on individual mooring hooks. By electronic means the load signals can be transmitted to ship and Jetty control rooms and alarms may be fitted. By this means tne Jetty can advise the ship when critical situations are developing. It has been found, from an operational viewpoint, that the interpretation of system-information must be used with care. Information should not lead to an over-reaction on the part of terminal staff or ships’ officers. Before such systems are put into practice it is recommended that ships’ officers and Jetty operators be properly trained in how best to interpret the information.

A recent event in Europe highlighted some of the foregoing difficulties and an investigative report on the incident was made available to SIGTTO members. The check lists annexed to SIGTTO’s letter are reproduced in Appendix 3***.

In devising mooring plans a number of reports have shown that sometimes extra-special care has to be taken to cover the need for adjusting moorings during cargo handling. (Such adjustments are often necessary due to changes tn tidal height). Unless all mooring lines are positively deployed to provide suitable retaining power, as a rope Is being slackened for adjustment – for a short time – there may be limited restraint and the ship may move along the berth. To date such movements have been limited to a maximum of about one metre – but are considered indicative of a critical happening. This problem can be overcome by selective deployment of appropriate mooring lines in the mooring plan. In some cases this may mean that a number of mooring lines are orientated in a more longitudinal direction than would otherwise have been the case. Investigation of this question can only be subject to computer analysis on an individual port by port basis.

The listing of known ship break-outs is to be found in the appendices. This listing (with one exception) suggests that the main problems occur at terminals handling ships of over 50 000 m³ capacity. It is concluded that few berths are immune from the break-out problem – see also Section 9***.